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EOSC 114 - Storms
Day 2-05 Time-lapse of thunderstorm evolution & lightning 2015 (3.75 minutes, Pecos Hank) play first half at normal speed; 2nd half play faster
https://www.youtube.com/watch?v=U9m9XVmfrxU
Other YouTube Videos you can watch on your own. (not testable):
Day 2-01 Time-lapse of 2015 supercell storm chase. (5.5 minutes) play at fast speed
https://www.youtube.com/watch?v=LYubHpEMTPM
LG 2a-d
A video “Teaser”, while students enter the classroom.
Day 2 - Video 00 - Monsoon IV. (8:08)
https://www.youtube.com/watch?v=LbY3DdzV0rA
video by Mike Olbinski
1
(not testable):
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•More Thunderstorm Fundamentals- Observing Tstorms, with satellite & radar- Squall-line thunderstorms- Supercell thunderstorms & mesocyclones
•Thunderstorm Hazards: downpours of rain &downbursts of air
•B. Moist air – the fuel for storms
Outline for Today
The Turbulent Atmosphere (Storms)
Prof. Roland Stull
© by Wolf Read, used with permission
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Today’s Learning Goals (LG: 2a-e)
By the end of this period, you should be able to:
2a) list and describe the storm hazards and disaster scales covered in this course.
2b) name and describe the characteristics and hazards of squall lines and of the 3 main types of supercell thunderstorm.
2c) use images and videos from weather radars (reflectivity & Doppler velocity) and satellites (visible & infrared) to identify storm characteristics and anticipate storm changes.
2d) identify downbursts and gust fronts, describe how they form and look, and what their hazards are.
2e) explain how humidity, saturation, latent heat, advection, and adiabatic cooling affect storm energy.
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Observing and Monitoring using Remote Sensors
Satellite
Radar
scijinks.nasa.govUSGS
LG 2c
A remote sensor is an instrument that is remote from (outside of) the storm, but can
measure the storm.
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Recall this photo from last time. Note the oval shape of the anvil cloud.See the shadow under the anvil cloud.See the lumpy region of updraft overshoot, which pin-points the violent stem portion of the mushroom cloud. These are clues to help identify Tstorms from satellite images.
NASA
LG 2cView from Space
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25 June 2003. UCAR / RAP
Colorado
South Dakota
Minnesota
Iowa
Kansas
Nebraska
Wyoming
Satellite Visible Image of Tstorms (Satellites see the top of the anvil cloud)
LG 2c
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Thunderstorms observed from Space
Thunderheads near Borneo, Indonesia are featured in this image photographed by an Expedition 40 crew member on the International Space Station. Credit: M. Justin Wilkinson, Jacobs and Michael Trenchard, Barrios Technology at NASA-JSC. 5 Aug 2014. NASA.
LG 2c
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Satellite visible time-lapse of a 2017 Thunderstorm evolution (1:00):
Day 2 Video 32:
http://rammb.cira.colostate.edu/dev/lindsey/loops/24may14_g14_vis_texas_loop.mp4
Satellite Videos of Thunderstorm Growth & Hurricane Evolution
from new GOES 16 & 17 Satellites
LG 2c 8
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2019/09/190901_goes16_visible_infrared_30second_Dorian_anim.gif
Satellite visible & IR time-lapse of (2019) Hurricane Dorian evolution (1:00):
Day 2 Video 33 (view in web browser):IR = infrared.
High altitude cloudsare highlighted in red, because
these are often the tops of dangerous thunderstorms
Visible images show clouds during daytime only.IR images can show clouds both day and night.
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Radar Image of Thunderstorm Cells
(radar sees the precipitation inside the storm; namely,in the up- & downdraft stem of the mushroom cloud)
from NWS
Tornado Outbreak in Oklahoma, 3 May 1999)
LG 2a,c
Radar
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dBZ: A Disaster Intensity Scale for
Radar-echo
Strength
(an indicator of Rainfall-
Rate)
© by Roland Stull
LG 2a,c
dBZ = radar echo intensity (in decibals).
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Radar Loop (video) of Thunderstorms
dBZ
By tracking past movement of Tstorm cells
on radar, we can warn people in their paths.
NWS
LG 2a,c
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Weather Radar Damaged by winds in Hurricane Irma 2017
NWS - Puerto Rico
LG 2c
before
after
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Road-map to Storm topics
Day HazardsRisk & Safety
FundamentalsAppearance & Evolution
Energymakes storms
1 LightningThunderstorm
basicssun, radiation,
surface heating
2 Rain Downpours,Air Downbursts
Supercells, mesocyclone. Observ.: radar, satellite
moisture, condensation, latent heating
3 TornadoesWall cloud, striations,
Doppler radar
4 HailClouds at Tstorms:
flanking line, mammatusheat to motion, forces, winds
5 Flooding, winds, waves, storm surge Hurricanes
energy in warm ocean, Coriolis
Learning Goals (LG): 1-5
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cumulonimbus (thunderstorms) are made of large cells that evolve during 15-30 min.
most thunderstorms (thunderstorms) contain 2 or more cells, and are called multicell thunderstorms
squall line - a line of thunderstorms
sometimes a very large, rotating single-cell thunderstorm forms, called a supercell thunderstorm. They can cause the most violent tornadoes, large hail, frequent lightning, heavy rain, strong winds. A rotating thunderstorm is called a mesocyclone.
Supercell types: low precipitation , classical , high precipitation
Thunderstorm Cells : Squall lines & Supercells
First
LG 2a,b
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Squall Line Thunderstorms
LG 2b
Squall Line Thunderstorms
• Consists of many thunderstorms in a line; hence, these storms are “linear”, or somewhat-linear (“quasi-linear).
• Often forms along a cold front.
cold front movement
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Squall Line Thunderstorms
LG 2b
Squall Line Thunderstorms
• Consists of many thunderstorms in a line; hence, these storms are “linear”, or somewhat-linear (“quasi-linear).
• Often forms along a cold front.
cold front movement
thunderstorm
movement
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Squall Line Thunderstorms
LG 2b
Squall Line Thunderstorms
Video 2 - 07. Storm of Beauty (Pecos Hank , Watch only the first 3:00 minutes)
• Consists of many thunderstorms in a line; hence, these storms are “linear”, or somewhat-linear (“quasi-linear).
• Often forms along a cold front.
https://www.youtube.com/watch?v=0jkfnIBJRBQ
cold front movement
thunderstorm
movement
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cumulonimbus (thunderstorms) are made of large cells that evolve during 15-30 min.
most thunderstorms (Tstorms) contain 2 or more cells, and are called multicell thunderstorms
squall line - a line of thunderstorms
sometimes a very large, rotating single-cell thunderstorm forms, called a supercell Tstorm. They can cause the most violent tornadoes, large hail, frequent lightning, heavy rain, strong winds. A rotating Tstorm is called a mesocyclone.
Supercell types: low precipitation , classical , high precip.
Thunderstorm Cells : Squall lines & Supercells
LG 2a,b
18
Next
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Supercell Videos from YouTube
Three types of supercell: (1) low precipitation (LP) supercell. It can produce lots of hail.
(2) classic supercell, (with rainy downdraft & rain-free updraft)
(3) high precipitation (HP) supercell, updraft mostly surrounded by rain.
Some are in-between or contain features of 2 or more types, and are called “hybrid” or “mixed mode” storms.
Day2-08 Overview of Supercells (Pecos Hank , 4:30)
LG 2b
https://www.youtube.com/watch?v=yvIKIgelY6g
Watch on your own:
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Supercell Videos from YouTube
Three types of supercell: (1) low precipitation (LP), but produce lots of hail.
(2) classic, (with rainy downdraft & rain-free updraft)
(3) high precip. (HP), updraft mostly surrounded by rain.
Some are in-between, and are called “hybrid” storms.
Day2-10 LP in 2012 (5 min, play fast) https://www.youtube.com/watch?v=2HBP9TNl-Io
Day2-15b LP in 2016 (show from 0:25 - 0:45)
LG 2b
Watch on your own (Not testable):
20
https://www.youtube.com/watch?v=Xn1i4aKw30s
https://www.youtube.com/watch?v=ZxH_tOZ3PS0LP in 2013 (1:45 min)
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Day2-20 Classic at Brisbane, Australia. Nov 2013 (2:30)
Day2-25 Classic at Booker time lapse. 3 June 2013 (1:50)
https://www.youtube.com/watch?v=o1eP5WVM5bQ
https://www.youtube.com/watch?v=ak05BQ6eNLU
Watch on your own (Not testable):
21
Day2-23 Classic mesocyclone in South Dakota, Aug 2017. (0:36)
https://www.youtube.com/watch?v=8rtBX09inw0
Supercell Videos from YouTube
Three types of supercell: (1) low precipitation (LP), but produce lots of hail.
(2) classic, (with rainy downdraft & rain-free updraft)
(3) high precip. (HP), updraft mostly surrounded by rain.
Some are in-between, and are called “hybrid” storms.
LG 2b
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Day2-35 HP supercell in Texas. 2015
Day2-30 Hybrid supercell in Lamar, CO timelapse. 2015https://www.youtube.com/watch?v=L60AHze111o
https://www.youtube.com/watch?v=trVMTXoDPGA
Hybrid Supercell. Watch on your own (Not testable):
22
Supercell Videos from YouTube
Three types of supercell: (1) low precipitation (LP), but produce lots of hail.
(2) classic, (with rainy downdraft & rain-free updraft)
(3) high precip. (HP), updraft mostly surrounded by rain.
Some are in-between, and are called “hybrid” storms.
LG 2b
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Thunderstorm Hazards• lightning• tornado• hail• downpours (of rain) / local flooding• downbursts (of air) / gustfronts
Hurricane Hazards• contain thunderstorms• storm surge / coastal flooding• high waves• coastal erosion
todaytoday
LG 2a,d
1. Storm Hazards covered in this course
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© by Roland Stull
Downpoursof rain can
causeFlash
Floods
LG 2a,c
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NWS Animation of flash floods vs cars (1:00)
Day 2 Video 45:
Flash Flood Safety
LG 2c
https://www.youtube.com/watch?v=eI6mIlHKrVY
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Downbursts & Gust Fronts (of air)
• Downdraft speeds of 20 to 90 km/h.
• Horizontal wind speeds near ground of up to 250 km/h.
• Microbursts are small diameter (" 1 km) downbursts.
Side view:
© by Roland Stull
LG 2a,d, 4a
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Hazards: Downbursts & Gust Fronts
! What: Downburst - cold (dense) air sinking.
! Why: Tstorm can create dense air where rain falls;due to evaporative cooling.
! Risks: Often invisible, but a hazard to aircraft.
! What: Gust front - leading edge of cold, horizontal straight-line winds.
! Why: downburst air hits ground & spreads outward in straight lines.
! Visible: haboob (if dry ground); arc cloud (if moist air); gustnado
! Risks: can blow down large trees and destroy weak structures (mobile homes; out-buildings); hazard to aircraft during take-off/landing.
! Safety: avoid weak bldgs & trees that could fall.Airports have sensors; flights avoid; pilots trained.
LG 2a,d, 4a
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Downbursts & Gust Fronts (of air)
Top view:
ground
straight-line
winds
Tstormup & down-
draft
gust front
arccloud
© by Roland Stull
LG 2d, 4a
gustnadoes28
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Downbursts & Gust Fronts (of air)
Top view:
ground
straight-line
winds
Tstormup & down-
draft
gust front
arccloud
straight-straight-
gust frontstraight-
linewinds
Tstormup & down-
draft
gust frontstraight-
gust frontstraight-
Anvil
© by Roland Stull
LG 2d, 4a
gustnadoes29
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Crash of Eastern Airline Flight 66.Killed 112 people at JFK airport in NY, 1975.
Downbursts & Gust Fronts (of air)
ground runway
Tstorm
1
23
XCrashSite
© by Roland Stull
LG 2a,d
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WeatherStock - used under license
Arc Clouds along Gust Fronts
arc cloud
arc cloud
WeatherStock - used under license
LG 2a,d, 4arain & downburst
rain & downburst
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Downbursts & Gust Fronts
Day2-50 Gust front 2013 Brisbane, AU (1:13)
Day 2-55 Gust front 2014 Dover, UK (1:13)
https://www.youtube.com/watch?v=qwKIq1fKSM8
https://www.youtube.com/watch?v=jJB05Hcjch8
Day 2-60 Shelf cloud 2010 at beach in MI (3:27 , play 5x speed)
https://www.youtube.com/watch?v=mOVwlfrKN2g
LG 2a,d, 4a
Watch on your own (Not testable).
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Haboobs (sand storms)
LG 2a,d, 4a
Another Hazard:
D.Newton, wunderground.com33
NWS, Phoenix
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Video Clips
Haboobs / Dust Storms
• Day 2-70 Driving into dust storm in AZ (9:56)
• Day 2-65 Dust storm in Iraq (2:33, play 5x)https://www.youtube.com/watch?v=iC2qlU8G8vw
https://www.youtube.com/watch?v=3glyRZLZAR0
• Day 2-75 News Report of 2011 storm AZ (4:45, view first 1.5 minutes)https://www.youtube.com/watch?v=RD5I9UhbRgg
LG 2a,d, 4a
Watch on your own (Not testable):
• Day 2-80 Gustnadoes and Haboob (Pecos Hank)https://www.youtube.com/watch?v=vVlwbqglCDs
Day 2 - Video 48 Haboob segment (view only 6:15 - 7:40)Monsoon V video by Mike Olbinski
https://www.youtube.com/watch?v=TC75USRhdho
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virga
cloud
Stull vs. Downburst
planetpals.com
whitehorseair.com
LG 2a,d
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Insights
Instead of memorizing the end effects, if you understand the underlying causes & processes, then you can make predictions for new situations.
LG 1-5
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WeatherStock, used under license
B. Moist Air – the Fuel for Storms
Storm EnergyLG 2e
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Storms have special organizationand capability to: • draw in humid air, • then to cause it to condense, & • release its heat into the storm, • resulting in precipitation & violent winds
Thus, we need to look at concepts of: 1. humidity 2. saturation 3. latent heat 4. advection 5. adiabatic cooling
Storm Organization
A visible cloud has10 billion cloud droplets
in each cubic meter of air.
WeatherStock, used under license
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1. Humidity
Air = mixture of gases:
Humidity is the amount of water vapour in the air. There are many humidity variables (i.e., many ways to quantify humidity.)
• 0 to 4% of water vapour +
• 78% (±3%) of nitrogen +
• 21% (±1%) of oxygen +
• trace gases +
• liquid water droplets
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A Humidity Variable: Mixing Ratio (r)
Mixing ratio = theamount of water vapour
divided by the amount of all other gases:
Examples.
(1) If you mix 2 parts water vapour and 5 parts all other gases. Then mixing ratio is r = 2/5 = 0.4
(2) If you mix 78 parts of N2 + 21 parts of O2 + 1 part of H2O, then
mixing ratio is r = 1 / (78+21) = 1/99 = 0.011
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typical value
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watermolecules
sealedbox
Saturation = Equilibrium ofEvaporation & Condensation
• Water vapour is special -> can easily condense into liquid. • Constant exchange of H2O molecules occurs between vapour & liquid:
· (vapour to liquid) = condensation · (liquid to vapour) = evaporation
• The mixing ratio tends to approach an equilibrium where condensation matches evaporation. This equilibrium is called saturation.
• For all practical purposes, saturation value is maximum humidity that air can hold .
2. Saturation – an Equilibrium between Evaporation & Condensation
© by Roland Stull
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Saturation value is important in controlling atmospheric humidity. • Warmer air can hold more water vapour at equilibrium than colder air !!!!! • Air that contains this max amount = saturated(i.e., cloudy or foggy) • Air holding less = unsaturated (i.e., not cloudy)
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0.010
0.020
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-30 -20 -10 0 10 20 30 40 50
Temperature (°C)
r (k
g/kg
)
Saturation Mixing Ratio (rs)increases exponentially with
Temperature (T)
rrs
satu
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© by Roland Stull
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3. Advection & Adiabatic Cooling
• When a thermal of unsaturated air rises adiabatically (with no heat transfer to the surrounding environment), the thermal cools roughly 10°C/km of rise.
• Cooler air can hold less water as vapour
• Therefore, some vapour must condense into liquid droplets.
• But condensation releases latent heat.
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Advection = movement of air by the wind.Water vapour can be advected into a thunderstorm by the wind.
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Storms strengthen whenlatent heat –> sensible heat.
If the Saturation Humidity value becomes smaller than the actual Humidity, then condensation occurs.
This condensation does 3 things:
• releases the stored latent heat back into sensible heat to make storms warmer,
• reduces the humidity down to the equilibrium (saturation) value, &
• produces or increases liquid cloud drops, which can grow to become rain drops.
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Summary of Day 2
Next Class - Tornadoes
The Turbulent Atmosphere
Prof. Roland Stull
•More Thunderstorm Fundamentals 4. Squall-line & Supercell thunderstorms & mesocyclones 5. Observing Thunderstorms, with satellite & radar
•Downpours, Downbursts & Gust Fronts
•Moist air – the fuel for storms
© by Wolf Read, used with permission 45